1. Field of the Invention
This application is related to pending U.S. application No. 650,521, filed on Sept. 14, 1984 in the name of OHTA et al., entitled RECORDING APPARATUS.
The present invention relates to a recording apparatus in which electric optical converter elements such as liquid crystal light shutter and LED are incorporated, and more particularly, it relates to a recording apparatus which allows buffers to be eliminated from the external circuit of the recording apparatus.
2. Prior Art
The impact printer which impacts the ribbon on a sheet of paper to achieve mechanical printing has been used for a long time as a terminal instrument for computer outputs. This impact printer is excellent in the quality of letters printed and has high reliability, but it cannot meet the needs of customers because the printing speed and the amount of information have increased these days.
On the contrary, the non-impact printer which does not perform mechanical printing but produces images using electrostatic development or the like can achieve recording in free format basically by changing external inputs and therefore record symbols, lines and image information, in addition to character information. The non-impact printer employs one of the optical, magnetic, electrostatic and thermal recording manners, and the optical recording manner is the best to meet any of uses including from low to high speed operations.
In the case of this optical recording manner, light converter elements such as laser, OFT, LED and LCD are used to write image information on the light conductive recording body, but the light scanning system for producing laser beam becomes complicated when the laser is used, and the laser device is expensive. In addition, there is a problem of how the stability of laser beam output is matched with the light conductive recording medium. More specifically, the luminous wavelength of laser ranges 630-820 nm and is shifted from the spectral sensitivity range of the light conductive recording body which is usually used by the copying machine, so that sensitivity lack of the light conductive recording body always presents a problem. When sensitisation is made to the side of long wavelength to compensate the sensitivity lack, the light conductive recording body becomes too sensitive to environmental conditions such as temperature. The recording apparatus in which the liquid crystal light shutter are incorporated can be cited as one to eliminate the above-mentioned drawbacks.
The liquid crystal light shutter will be described. Two driver modes of the guest-host effect mode (which will be hereinafter referred to as GH effect mode) and the twisted-nematic effect mode (which will be hereinafter referred to as TN effect mode) typical in the electric optical effect of liquid crystal will be described at first.
FIGS. 1(A) and 1(B) are intended to explain GH effect mode while FIGS. 1(C) and 1(D) TN effect mode. The liquid crystal cell of GH effect mode comprises solving a guest dye in the host liquid crystal. As shown in FIGS. 1(A) and 1(B),, for example, incident light 1 which is natural light becomes a light 3 which has been linearly polarized by a polarizer 2 such as Nicol's prism and Gramthomson's prism to enter into a liquid crystal cell 4. The liquid crystal cell 4 consists of liquid crystal particles 5 and dichroic dye particles 6, and these liquid crystal and dichroic due particles 5 and 6 perform directional movement due to external electric field. The dichroic dye particles 6 absorb more light in their major axis than in their minor axis. Therefore, the linearly polarized light 3 which is incident upon the liquid crystal cell 4 is absorbed to emit no light outside when the liquid crystal and dichroic dye particles 5 and 6 are arranged as shown in FIG. 1(A). This means that the liquid crystal cell 4 is closed when it is used as a liquid crystal light shutter. When the liquid crystal and dichroic dye particles 5 and 6 are so arranged as not to absorb the incident light 3 as shown in FIG. 1(B), a light 7 is emitted from the liquid crystal cell 4. This means that the liquid crystal cell 4 is opened when it is used as the liquid crystal light shutter.
A liquid crystal cell 8 shown in FIGS. 1(C) and (D) comprises arranging its liquid crystal particles 9 parallel to the panel plane, twisting it by 90 degrees between electrodes, and sandwiching it between two polarizers 10 and 11. The positioning of the polarizers 10 and 11 relative to the polarizing plane is done according to the homeotropic nicol arrangement as shown in FIGS. 1(C) and 1(D) as well as the parallel nicol arrangement. The opened and closed operations of the liquid crystal cell in the parallel nicol arrangement becomes opposite to those in the homeotropicnicol arrangement which will be described below. In FIG. 1(C), incident light 12 is linearly polarized by the polarizer 10 to enter into the liquid crystal cell 8 of the TN effect mode. Since the liquid crystal particles 9 are twisted by 90 degrees, the polarizing plane of output light 14 is turned by 90 degrees when it receives light 13, to thereby enter the light 14 into the polarizer 11. Since the plane by which the light 14 is polarized is parallel to the polarizing plane of the polizer 11, the light 14 can penetrate through the polizer 11 to thereby emit light 15, which means that the liquid crystal cell 8 becomes opened as the liquid crystal light shutter.
When the liquid crystal particles 9 are vertically arranged as shown in FIG. 1(D), the output light 14 which is not optically rotated in the liquid crystal cell 8 of the TN effect mode is made perpendicular to the polarizing plane of the polarizer 11. Therefore, the output light 14 cannot penetrate through the polarizer 11, which means that the cell 8 becomes closed as the liquid crystal light shutter.
The method of driving this liquid crystal light shutter will be described next. Double frequency drive is usually used to drive the liquid crystal light shutters.
The double frequency drive is intended to rearrange the liquid crystal particles, changing the frequency of electric field and using its inversion due to dielectric anisotropy. As shown in FIG. 2, for example, the dielectric anisotropy .DELTA..epsilon. becomes positive in the case of a frequency (which will be hereinafter referred to as f.sub.L) lower than a crossover frequency (which will be hereinafter referred to as f.sub.C). On the contrary, the dielectric anisotropy becomes negative in the case of a frequency (which will be hereinafter referred to as f.sub.H) higher than the frequency f.sub.C. When a signal having the frequency f.sub.L is applied, the liquid crystal particles are arranged parallel to the electric field, while when a signal having the frequency f.sub.H is applied, they are arranged transverse to the electric field.
The dielectric anisotropy .DELTA..epsilon. is sensitive to viscosity and therefore changes largely responsive to temperature change. When viscosity changes, the frequency f.sub.C also changes. When temperature rises from 20.degree. C. to 40.degree. C., for example, the frequency f.sub.C also rises from 5 KHz to 46 KHz. When viscosity is low, therefore, the action of the liquid crystal particles becomes so quick that high speed response can be expected. It is therefore desirable that temperature is raised to some extent when used.
Providing that the size of transferring sheets employed by the recording apparatus is A3 and that recording density is 10 dots/mm, a micro-shutter having a capacity of about 3000 dots/row will be needed. When the liquid crystal light shutters having a large recording capacity like this are to be statically driven, driver elements, number of lines and packaging area are increased to thereby make the cost higher and also make it difficult to package the number of lines and their connection.
The above-mentioned drawbacks could be conventionally reduced by time-sharing drive. However, this time-sharing drive caused the following problem.
The object of the time-sharing drive performed by the display means is eyes of people and therefore, the drive may be done, keeping the display so bright as not to make the eyes of people feel discomfort because of flickering, for example. Therefore, the number of time-sharing, writing cycle and the like are determined by the response speed of display elements, magnitude of output energy, display capacity and the like.
The time period which is assigned to a selected group by conducting n-time-sharing drive is shorter than Tw/n, providing that the writing cycle is Tw. When n-time-sharing drive is applied to the liquid crystal light shutters according to the conventional manner, therefore, the time during which the liquid crystal light shutters are opened becomes less than 1/n and the amount of exposure which is applied to the photoreceptor also becomes less than 1/n, so that lack of light quantity becomes severer as the number n of time-sharing drive becomes larger.
In a case where the liquid crystal light shutters 16 aligned on a line are grouped into m units, the write selecting electrodes are n units including C.sub.1 -C.sub.n, the recording signal electrodes are m units including S.sub.1 -S.sub.m, the moving or subscanning direction of the photoreceptor is represented by 17 in FIG. 3(C), and the time-sharing drive is performed as shown in FIG. 3(B), the write selecting electrodes C.sub.1, C.sub.2,-C.sub.n are selected at a timing A.sub.1, A.sub.2,-A.sub.n, respectively, to perform recording. The liquid crystal light shutters 16 aligned on a line are to be recorded as shown by a broken line 18 in FIG. 3(C), but they are recorded inclined as shown by solid lines 19 in FIG. 3(C) because their recording times are different from one another, depending upon the time-sharing drive. The degree of this inclination 19a represents the moving distance of the photoreceptor drum which moves for the writing cycle Tw.
In the case where the liquid crystal light shutter are employed, the time-sharing drive which is performed in same manner as in the case of the display means is not satisfactory because of reduction of exposure and from the viewpoint of recording quality, as described above.
The driver circuit for time-sharing drive of the liquid crystal light shutters also needs delay and composite circuits. In the case of conducting n-time-sharing drive, for example, it is necessary to produce mixed recording data, which comprises delaying data, which is applied to each of the liquid crystal light shutters, by 1/n for the writing cycle Tw. FIG. 4 A is a block diagram showing a circuit for producing this mixed data.
An image signal generator section 20a generates a time-belonging picture element signa) 20C, synchronous with the rising of a clock pulse 20b, and this time-belonging picture element signal 20C is sent to an MUX gate 20d and applied, at the same time, to a data delay section 20f in which k-unit of m-bit shift registers 20e are connected in serial to delay k lines. k is 3 in the case shown in FIG. 4. A data signal 20g which has been delayed at the data delay section 20f, corresponding to the k lines is inputted to the MUX gate 20d and mixed with the time-belonging picture element signal 20c to produce a recording data 20h. This recording data 20h is controlled by the clock pulse 20b inputted to a D type FF 20i and also by a signal 20p generated by a transferred enable signal 20j.
The clock pulse 20b is also supplied to an AND gate 201 via an inverter 20k and cooperated with the transferred enable signal 20j to generate a clock pulse 20m, which is supplied to a liquid crystal light shutter driver circuit. When the mth-bit of the mixed recording data 20h which corresponds to one line is sent to the liquid crystal light shutter driver circuit, synchronous with the rising of the clock pulse 20m, a latch pulse 20n is generated at the image signal generator section 20a and supplied to the liquid crystal light shutter driver circuit, so that data which corresponds to one line is shifted to the data latch in the driver circuit, thereby causing the shift register to be made free and ready for an input applied from the subsequent line.
In FIG. 4(B), a symbol * represents a data which has been delayed by the k lines (k is 3 in this case).
Depending upon the way of supplying the recording data, two manners can be imagined to form the driver circuit, and which manners are shown in FIG. 5 as driver circuits 90 and 103. It is assumed that the total number of the liquid crystal light shutters 88 and 89 is m (which is an even number). The driver circuit 90 comprises an m-bit shift register 91, m-bit data latch 92, m-bit data selector 93, level shifter and high voltage drivers 94a and 94b. The m-bit shift register 91 alternately receives for the writing cycle Tw the m-bit of the recording data relative to the liquid crystal light shutter 88 and the m-bit of the recording data relative to the liquid crystal light shutter 89 which has been delayed by the k lines to compensate the positional error between the liquid crystal light shutters 88 and 89. One of recording data lines 95 is selected by the data selector 93, according to the mixed recording data shifted to the data latch 92 responsive to a latch pulse 92a, and it is sent to the level shifter and high voltage drivers 94a.
On the other hand, a write selecting signal 96 is inputted, as write selecting signals 98 and 99, to write selecting electrodes of the liquid crystal light shutters by means of the level shifter and high voltage drivers 94b. To explain signals inputted to recording signal electrodes more concretely, a mixed recording data 101 is inputted to the m-bit shift register 91, synchronous with a writing cycle signal 100, and shifted to the data latch 92 responsive to a latch pulse 102, as shown in FIG. 7. The recording signals 95 which correspond to the liquid crystal light shutters 88 and 89 are selected by the data selector 93, and one of the recording signals 95 is inputted to the recording signal electrode through the level shifter and high voltage drivers 94a.
Another example of the driver circuit which is represented by numeral 103 in FIG. 5 comprises an m/2-bit shift register 104, m/2-bit data latch 105, m/2-bit data selector 106 and level shifter and high voltage drivers 94a and 94b. The recording data relative to the liquid crystal light shutter 88 and the recording data relative to the liquid crystal light shutter 89 which has been delayed by the k lines are separated to occupy the front and back halves of the writing cycle Tw, respectively, and then inputted. One of recording signals 97 is selected by the data selector 106, responsive to the separated recording data shifted to the data latch 105, and it is sent to the level shifter and high voltage driver 94a. More specifically, a recording signal 110 which has been separated as signals 108 and 109 synchronous with the writing cycle signal 100 is received by the shift register 104 and shifted to the data latch 105 responsive to a latch pulse 111, as shown in FIG. 7. The recording data 110 is then inputted to the recording signal electrode, as described above. The recording data 108 is for the liquid crystal light shutter 88, while the recording data 109 is delayed by the k lines and for the liquid crystal light shutter 89 which is separated by a distance l from the shutter 88.
As apparent from the two above-described examples, 2.sup.n-1 kinds of driver signals are supplied at the time of non-selection in the n-time-sharing drive, whichever driving manner may be employed.
When the above-mentioned driver circuits 90 and 103 are employed in the time-sharing drive, the driving state for a selection period Tw/n can be kept during a non-selection period (1-1/n)Tw of the write selecting signal electrodes and operate apparently like static drive to prevent the exposure time to be reducded remarkably. The manners shown in FIGS. 4 and 5 is required to be used to produce the mixed recording data shown in FIG. 6, as described above.
The micro-shutters are usually arranged in zigzag in the liquid crystal light shutter, and when m units of the micro-shutters are arranged in it, delayed k lines, the bit number of the shift register 20e shown in FIG. 4A becomes m by k.
In order to do recording on a sheet of A3 size at a recording density of 10 dots/mm, for example, about 3,000 units of the micro-shutters are needed, and the shift register having a capacity of 9,000 bits is needed to achieve the 3-line delay. When a RAM (or random access memory) is employed, this capacity may be doubled.
Because the shift register and the RAM having this capacity were used as elements different from each other, the print plate became large and wires were needed between these elements, thereby making it troublesome to package the liquid crystal light shutter driver circuit.